It has been suggested Dy some studies of lower eukaryotes and human chiasmata that there is positive genetic interference at centromeres. The data at the molecular level are lacking in humans because only recently have human DNA probes which localize to specific centromeres become available. The long-term goal of this project is to determine and compare the genetic and physical distances of DNA sequences proximal to and at the human centromeric region. The following strategy will be utilized to map these probes: Physical and genetic maps will be determined between DNA sequences which localize to the centromere, between these centromeric markers and pericentromeric DNA sequences on either the long arm or short arm of the chromosome, and between DNA sequences which are on either side of the centromere of a given chromosome, i.e. spanning the centromeric region. The source of DNA sequences will be single copy and repetitive sequences which are present at the centromeric region of specific human chromosomes X, I, 6, 7, 13, 15, and 22. Other sequences around the centromeric region will be isolated by walking in chromosome specific libraries. Adjacent or overlapping DNA fragments will be isolated by pulse field gel techniques and cloned into bacteriophage and YAC vectors. To create a restriction map of the centromeric region, physical distances will be determined between sequences by probing digests of genomic fragments separated by conventional gel electrophoresis and pulse field gel techniques. Appropriate genomic digests will determine the organization and location of DNA sequences. Genetic distances will be estimated by computer linkage analysis using polymorphic markers (DNA, serum proteins, enzymes, etc.) segregating in large three generation families. The comparison of high resolution genetic and physical mapping of the centromeric regions may elucidate differences at the centromere as compared to other regions of a chromosome and between certromeres of different chromosomes. This may suggest significant functional differences in the behavior of various chromosomal regions at meiosis.